Raisable landing gear is already known of the type that comprises a shock absorbing strut hinged to the structure of an airplane, and including a sliding rod that carries a wheel set, the landing gear also including a hinged side-brace with two alignments: a main alignment that connects the shock absorber strut to the airplane structure and comprising an upper arm hinged to a lower arm; and a secondary alignment connecting one of the arms of the main alignment to said airplane structure, and likewise comprising an upper arm hinged to a lower arm, unlocking means also being provided to break the secondary alignment and consequently to break the main alignment when the undercarriage is raised.
In order to make the organization of such landing gear easier to understand, together with the problems that can be encountered with the type of unlocking means used, FIG. 1 of the accompanying drawings shows a conventional raisable landing gear of the above-specified type, said landing gear being shown in the lowered position so as to enable its component parts to be distinguished more clearly, and in particular so as to show its hinged side-brace having two alignments (with the position of the landing gear in the raised position also being shown in order to complete the drawing).
From FIG. 1, it can be seen that raisable landing gear T has a shock absorber 100 constituted by a shock absorbing strut 101 and a rod 102 slidable coaxially within said strut. The top of the shock absorber strut 101 is hinged (at 103) to the structure S of the airplane, with the hinge axis passing through the end of a link branch 107 secured to said strut. A brace element 106 is associated with the shock absorber 100, said element being connected firstly via a rotary hinge 108 to the end of the link branch 107 and being hinged secondly at 109 on a bottom appendix of the shock absorber strut 101. The brace element 106 is also hinged at its bottom end 110 to a rotary sleeve 111 which is connected via a scissors linkage (having two arms 112 and 113) to the chassis 105 of a hinged wheel set 104 provided at the bottom end of the sliding rod 102. A driving actuator 115 serves to raise or lower the landing gear T, with the cylinder 116 of said actuator 115 being hinged on a middle appendix 114 of the brace element 106 while the rod of said actuator is hinged at its end 117 to the structure of the airplane. There can also be seen a wheel 118 disposed at the end of an appendix provided on the bottom portion of the strut, which wheel co-operates when the landing gear is raised with the hook of a catch box 119 housed inside the structure of the airplane.
The landing gear T is also fitted with a hinged side-brace 120 having two alignments. In the undercarriage-lowered position shown in FIG. 1, the component members of said hinged side-brace can be seen clearly, and in particular its main alignment 121 and its secondary alignment 131.
The main alignment 121 connects the shock absorber strut 101 (via a hinge 125 which is also associated with two connecting rods 126 and 127) and it comprises an upper arm 122 and a lower arm 123 which are hinged together at a hinge 124. As for the secondary alignment 131, it connects an arm (in this case the upper arm 122) of the main alignment 121 (via a hinge 135) to the structure of the airplane (at a hinge 136 associated with one end 128 of the above-mentioned fixed connecting rod 126), and it is also constituted by an upper arm 132 and a lower arm 133 which are hinged together at a hinge 134.
Unlocking means 140 are also provided to break the secondary alignment and thus to break the main alignment when the landing gear is raised. As shown herein, this unlocking means 140 is conventionally implemented in the form of a small actuator whose cylinder, in this case, is hinged at 141 to the upper arm 122 of the main alignment 121, while the rod thereof is hinged at 142 to the lower arm 133 of the secondary alignment 131.
When the driving actuator 115 is actuated to lower the landing gear, the small actuator 140 associated with the side-brace 120 follows the deployment motion of the two alignments 121 and 131, said motion generally being assisted by the presence of two traction springs 137 connecting the upper arm 132 of the secondary alignment 131 (at 138) to the airplane structure (at 139). In contrast, the landing gear is being raised, the small actuator 140 associated with the side-brace 120 is activated to retract its rod and thus break the secondary alignment 131 against the force of the return springs 137, thereby breaking the main alignment 121, and thus enabling the driving actuator 115 to operate normally.
Such a system is in widespread use, however it nevertheless suffers from a drawback inherent to the use of a small actuator as the unlocking means enabling the two alignments of the hinged side-brace to be broken. It is not possible to completely avoid the possibility that the locking means will become jammed, and the small actuator may seize up specifically when the instruction is given to raise the landing gear (said actuator merely following while the landing gear is being lowered).